Foundry sand additive



United States 2,828,214 FOUNDRY SAND ADDITIVE' Otto J. Myers, Morningside, and Erwin A. Olson, Edina, Minn., assignorsto Archer-Daniels-Midland Company, Minneapolis, Minn., a corporation of Delaware No Drawing. ApplicationJunels, 1953 SerialNo. 361,846

4 Claims. (Cl, 106-385) .mass which may'thenbe formed into the desired, shapes conforming with a pattern of the shape to be cast in metal, Thereafter, the molten casting metal is poured into thernold and after the casting hashardened and cooled the mold is removed and broken up for re-use. This invention relates particularly to an improved finely divided cellulosic agent for addition to foundry mold and. core. compositions and most especially to an additive for such compositions comprising the material obtained by grinding the woody pulp, known as shive, remaining after the liberation of the fibers from flax straw and other plants. The invention relates as 'well to methods of making molds and cores utilizing compositions con.- taining such plant shive material as an additive. V

Molding sands, particularly of the so-called synthetic type, exhibit a great deal of; strength and rigidity temperature range of 1000 F. and upwards. This characteristic, coupled with. the inherent expansion of the sand grains at these temperatures, results in a rupture of the mold wall resulting in casting defects identified as rat-tails, buckles and scabs. These are. all irregular protuberances on a casting caused by a break in this mold. Use of finely ground plant shive and particularly flax shive in the molding and core compositions has been found to reduce the rigidity of the mold Wall allowing it to deform under thermally induced stresses rather than to rupture and fail. The-use of flour made from shive in the mold composition also serves toreduce the expansion of the whole mold surface by being readily atent inthe" and rapidly burned out so as to allow space for the whole sand grains to expand individually. This stabilizing effect has been found to be helpful in obtaining relief from the aforementioned troublesome casting defects.

In cases where a comparatively heavy sectional core is wholly or partly surrounded by meduim to light sectioned casting, the core must lose strength rapidly to avoid setting up stresses in the metal which can tear or crack the cooling, contracting casting. It has been found that by the addition of finely divided shiveto thecore sand that collapse of the core ismaterially accelerated, thus protecting the casting from thisdamage.

As the finely divided shive material burns out of the sand it absorbsoxygen in the mold. This tends to inhibit metal oxidation at high temperatures and results in a lesser tendency for the surface metal to penetrate into the sand causingrough appearing castings andlhus re,- duces the attendant high cleaningcosts.

T he d t n. of h v f r to, molding. sandsimnroves. sand flowability hereby promoting smoo her, moretrue: to-pattern castings with a minimum of ramming. energy;

ice

2, Thatis, the addition of a small amount'of shive enhances the property of foundry sands whichcauses the sand to flow against the pattern and into pattern recesses under .rnoldingpressures. I

It; has also been found that the addition of shives lowers the dry. and hot strengths of sands. This means that the castings: are more easily shaken out of the, sand, and that the molding sand is easily reconditioned, being freefrom hard lumps.

The addition of the finely ground shive additive, to foundry molding sand compositions permits the sand to; be worked at a lower moisture range; without: inhibiting flowability of the molding sand. It also permits a denser mold to. be rammed without sacrificing thev ability of the mold to expand normally during founding.

The shiveadditive of this invention is particularly useful in core sand compositions that are used in connection 'with'thei. casting of non-ferrous light alloys, where the temperatures. involved. are somewhat lower and do not readily break down the usual care composition.

It'is. the principal object of this invention to provide an additive'comprising plantshives for. addition to foundry mold and: core compositions which will permit the attainment of the above recited beneficial results.

It is another object of this invention to provide an improved foundry sand molding and core composition comprising finely divided shive flour.

Still another object of this invention is to provide a novel and improved method of making molds and cores including the addition of a small amount of finely ground shive material in the foundry sand.

Other objects of this invention will become apparent as the description-proceeds.

To the accomplishment of the foregoing and related ends this invention then comprises the features hereinafter fully described and particularly pointed out in the claims, the following description setting forth, in detail certain iliustrative embodiments. of the invention, these being indicative, however, of but a few of the various ways inwhich the principles of the invention, may be employed.

Broadly stated, the invention comprises the addition to foundry sand compositions of a small amount of the cellulosicmaterial' obtained by grinding the woody pulp known as shive, which occurs in the stems. of various plants, notably those of the flaxplant (Linumiusitatissi-v mum). The shive is ground to. particle sizesv ranging from a few microns to'a size such that. substantiallyall of the particles willpass through a U. S. Series No. 40 sieve. The invention includes the use of foundry. sands containing this shive; material in. makingvmolds for'metal casting.

While the most available present source; of: shive material is the flax plant, other plant shive. material may be. used, such as. that obtained: from hemp, ramie and corn, sorgo. grainand like pithy materials.

Flax shive is the inner woody core, of the, flax straw whichremains after liberation of the outer fiber bundles. The stems of, the flax plant include an inner pulpy center aroundwhichithe long toughfibers are boundzby apectic gum. When grown for flax fiber, the; stems; of. the. flax: plant are usually subjected to a so-called rettingtreatment during which. they are. Wetted. and subjected. to bacterial action which dissolves the gums binding thefibers to the: shives. After drying the straw is: subjected to a soecalled scutching action which breaks up the brittle shivey material which; canthen readily fall away and be: separated from the tougher. resilient fibers, This isone source. of the; waste shive, material, which: ordinarily is discarded-or burned, but accordingto the presentinventionmay beused as: theadditive material;

A more common source (at least in the United States) of the flax shive material additive which can be used according tothe present invention is from fiax grown for seed (linseed). In such agricultural operation a shorter flax plant of less stemmy growth and more abundantly endowed with seed production is commonly grown. The flax is permitted to mature in the field and is then harvested, the straw being then a waste product, as it is hard, dry and does not even make good cattle bedding. As a result much flax straw has, in the past, been burned in the stack or in windrows in the field, although in more recent years mature seed flax straw has been baled and used as a source of fiber for cigarette and Bible paper. For such latter uses the flax straw is usually broken in a rough flaxbrake and the major'portion of the shives removed by mechanical operation, and the resultant liberated fiber is re-baled for shipment to the paper mills. .Again, the shives constitute a waste product, which according to this invention, are elevated'to usefulnessin commerce.

The flax shives as thus obtained from available sources are then ground in a hammer mill or other grinder and should be finely divided before addition to the foundry sand. Substantially all of. the shive particles, that is, at least 85%, should'pass through a U. S. Series No. 40 sieve, and no more than 2% should be retained by a U. S. Series No. 30 sieve. In other words, substantially all of the shive flour should have a smaller. Preferably, substantially all of the particle sizes should'range belowabout 60 mesh or will pass through a U; S. Series No. 60 sieve. The bulk of the shive particles should thus be between about 50 and 500 microns and preferably between about 50 and 300 microns with a minimum of finer or coarser particles.

The amount of ground flax shive which should be added to the foundry sand will depend upon the specific castings and the original condition of the sand. For most purposes this amount will vary between about ,4; and 2 /2% by weight of the dry sand. Normally, the shive additive will be included in amounts ranging from about /2 to 1 per cent by weight. Once the requisite amount of finely divided flax shive additive has been incorporated into a molding sand, subsequent additions are quite small, being just suflicient to replace that which has burned out.

It may be noted that in respect to core sand compositions there is used a sand which is relatively free from clay, but at least one binder such as cereals, oils or resins is used. In respect to molds, the binder is customarily clay, which may be separately added (for example, as bentonite) or a natural molding sand having a requisite natural clay content may be used. In all instances (cores particle size of 35 mesh or V and molds) there is at least one binder (cereal, oil, resin or clay) which, when activated by moisture, acts to hold the composition together during use.

In forming molds suificient water is added to the sand, clay and flax shive flour mixture to give the composition the desired plasticity to conform to the surfaces of the pattern. As in standard foundry practice the amount of water-which is added is usually gauged by the -foundry worker on the basis of proper temper, small amounts of water being added until the mixture has the desired consistency. Most generally, the amount of water required to reduce the dry sand, clay and flax shive flour mixture to the desired consistency ranges from about 2 /2 to 10 percent by weight and usually between about 3 to 7 percent.

In core sand practice, the common ingredients used are sand, one or more binders selected from gelatinized and/or dextrinized farinaceous products, core oils and resins (such asphenol-formaldehyde) and water. Sometimes small amounts of clay may also be used. A large variety of core oils are available commercially for this purpose and include various unsaturated polymerized oils, such aslinseed oil, China-wood oil, soybean oil, etc.,' oil compositions including a-heat-treated rosin and the like.

When employed in the foundry sand composition, the core oil is usually present in amounts ranging from about 0.5 to 2.5 percent by weight of the mixture. The farinaceous and resinous binders are present in an amount from about 0.5 to 2 percent. Moisture is added to proper temper ranging in amount from about 15 to 9 percent.

The shive additive is useful inre-used sand as well as in new sand composition. Where molding sand is re-used, as in the usual foundry practice, it is only necessary to add sufficient shivey additive to make up for what is burned out. Thus, as little as 0.25 percent additional shive is all that is necessary, in many instances.

Under some circumstances, such as if the finely ground flax shive is to be stored for long periods in a warm humid atmosphere it is desirable to incorporate a small but effective amount of a mold and fungus inhibitor in order to forestall the development of bacterial growth, mold, mildew, a musty or sour odor and the like, and in order to inhibit caking of the shive flour. The common mold and fungus inhibitors such as pentachlorophenol, cresol, paraformaldehyde and the like have been found to be effective when used in amounts ranging from about 0.05 to l percent'byweight, preferably about 0.1 percent, of the shives. The preservative may conveniently be added when the flax shives are being ground. Use of pentachlorophenol in amounts of about 0.1 percent by weight of the shives has been found to be 'especially effective in preventing mold growth, even during extended periods under severe tropical conditions.

The specifications of several typical and useful representative samples of shive material are given below in order to further illustrate, but not limit, the invention:

7 SCREEN ANALYSIS:

Particle sizes Percent of Various Size Shive Particles Retained U. S. Series Mesh Micron Shive Shive Shlve Equivalent Size Size Sample Sample B Sample 0 Number A 40 35 420 Trace 9.0 9. 4

Pan +270 53 5.9 8.4 0.1

Bulk density: 12 to 14 pounds per cubic foot. Moisture: 5 to 7 percent.

Proteinz3 to 6 percent.

Ash: 3to 8 percent.

Starch (Qualitative)i Negligible.

The'invention is further illustrated by means of the following exemplary foundry sand compositions in which all parts are by weighti Example I.Coarse core sand composition Parts Dry'coarse silica sand 95 Finely ground flax shive flour 1 Commercial fast-baking core oiL; 1 Commercial cereal binder; 1 Water 2 The dry sand cereal binder and flax shives are preferably first intimately admixed .in order thoroughly and uniformly to distribute theflax shives through the sand and thereafter the Water, and core oil are added. The

' composition was then rammed or blown into suitable core molds, and the green cores are then baked accord; ing to usual practice.

Example lI.Synthezic molding sand composition Parts Dry fine silica sand 89 Bentonite (Western) Finely ground flax shive flour 1.5 Water 4.5

The composition was then thoroughly mixed and placed against the pattern in suitable flasks, according to usual practice, the molds closed and metal poured.

Example lll.-Fine core sand composition Parts Dry silica sand 94 Finely ground flax shive flour 0.5 Commercial core il 1.5 Commercial cereal binder -Q 0.5 Water 3.5

The core composition is mixed according to the procedure of Example I.

Example lV.-Resin bonded core sand composition Parts Dry silica sand 96 Finely ground flax shive flour 0.25 Commercial phenol-formaldehyde resin so1ids 0.5 Commercial cereal binder 1.0

Water 2.25

The ingredients are intimately admixed and formed into a core as in Example I.

Example V.Natural molding sand composition Parts Naturally bonded molding sand (dry basis) 91.0 Finely ground flax shive flour 1.0 Water 8.0

tion only and the invention is limited only by the terms of the appended claims.

What we claim is:

1. Foundry mold and core sand material consisting essentially of silicon sand suitable for tempering with the addition of water in an amount of from about 1.5% to about 10% based on the weight of the sand and in combination, a flour of the inner pulpy center constituting the shive from the stem of plants selected from the group consisting of flax, hemp, ramie, corn, and sorgo grain of a particle size between microns to 500 microns in the proportion of about .25% to about 2.5% by weight of the sand and a binder in a proportion ranging from about 0.5% to about 2.5% by weight of the mixture.

2. The composition of claim 1 wherein the shive material is of a particle size in a range below about mesh and substantially all of the particles will pass through a U. S. Series No. 60 sieve.

3. The composition of claim 1 wherein the shive is from flax and at least about of the particles will pass through a U. S. Series No. 40 sieve and no more than about 2% will be retained by a U. S. Series No. 30 sieve and is present in proportion of about to about 1% by weight of the sand.

4. The composition of claim 1 wherein the shive is the flour of pulp from the center of flax stems and is of a bulk particle size between about 50 microns and about 300 microns with a minimum of fine and coarse particles.

References Cited in the file of this patent OTHER REFERENCES Dietert: Modern Core Practices and Theories, p. 105, 1942.

Clark et a1.: Modern Plastics, October 1945, pp. 158- 160, 214, 216, 218.

Clark: Modern Plastics, August 1949, pp. 111-115, 164, 165. 

1. FOUNDRY MOLD AND CORE SAND MATERIAL CONSISTING ESSENTIALLY OF SILICON SAND SUITABLE FOR TEMPERING WITH THE ADDITION OF WATER IN AN AMOUNT OF FROM ABOUT 1.5% TO ABOUT 10% BASED ON THE WEIGHT OF THE SAND AND IN COMBINATION, A FLOUR OF THE INNER PULPY CENTER CONSTITUTING THE SHIVE FROM THE STEM OF PLANTS SELECTED FROM THE GROUP CONSISTING OF FLAX, HEMP, RAMIE, CORN, AND SORGO GRAIN OF A PARTICLE SIZE BETWEEN 50 MICRONS TO 500 MICRONS IN THE PROPORTION OF ABOUT .25% TO ABOUT 2.5% BY WIGHT OF THE SAND AND A BINDER IN A PROPORTION RANGING FROM ABOUT 0.5% TO ABOUT 2.5% BY WEIGHT OF THE MIXTURE. 